This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The long-term goals of this project focus on defining mechanisms responsible for processing of the amyloid precursor protein (APP). Amyloidogenic processing of APP results in the generation of Abeta peptide fragments that are involved in the etiology of Alzheimer's disease (AD). The complete elucidation of the mechanisms that regulate APP processing has not been realized. We undertook a screen of ATP-binding cassette transporters expressed in the brain for their effects on APP metabolism. Our current results suggest that the ATP-binding cassette transporter (ABCA2) is a regulator of APP processing and Abeta production. Genetic evidence by single nucleotide polymorphism (SNP) mapping identified a single synonymous mutation in ABCA2 that is significantly associated with early-onset AD. We determined that ABCA2 overexpression in HEK293 cells bearing the APP Swedish mutation (APPsw) increased cellular APP holoprotein levels and Abeta secretion. Using microarray analysis of gene expression profiles in HEK293 cells stably transfected with ABCA2, we detected elevated levels of a number of genes associated with AD. The recent production of an ABCA2 knockout mouse will permit the unequivocal determination of the function of the ABCA2 transporter in regulating APP processing and Abeta production in vivo. A central hypothesis of this grant application is that ABCA2 functions in neuronal cells to regulate APP processing and Abeta production and thereby serves a critical role in maintaining homeostasis between amyloidogenic and non-amyloidogenic pathways of APP metabolism. In depth knowledge of the mechanisms of action of the ABCA2 transporter in vivo on regulation of APP processing will provide a critical basis for the development of therapeutic strategies to reduce Abeta burden in prevention and treatment of AD. This hypothesis will be investigating by pursuing the following the following specific aims: Specific Aim 1. Determine the role of ABCA2 in regulating APP processing and Abeta production in neuronal cells. Since we have previously demonstrated that ABCA2 regulates cellular APP holoprotein levels and Abetasecretion in non-neuronal HEK293 cells, we propose to investigate the specific hypothesis that ABCA2 may regulate APP processing and Abeta production in neuronal cells. Specific Aim 2: Determine the role of ABCA2 in APP processing and Abeta production through ApoE/low-density lipoprotein receptor-related protein (LRP) in neuronal cells. The ApoE4 allele is a strong genetic risk factor for AD and is a ligand for the low-density lipoprotein receptor-related protein, where it mediates esterification of HDL-derived cholesterol. LRP also mediates APP processing and Abeta generation. Since we report that ABCA2 regulates LRP expression in N2a neuroblastoma cells, perhaps by cholesterol trafficking, we propose the specific hypothesis that ABCA2 may regulate APP processing and Abeta generation through ApoE/LRP in neuronal cells.